Dynamics of oxygen in the YBa2Cu3O7-x basal planes by elastic-energy-loss measurements.

Abstract

We report elastic-energy-dissipation measurements in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathit{x}}$ from 50 to 300 K at frequencies between 0.48 and 6.3 kHz. It is shown unambiguously that the two peaks around ${\mathit{T}}_{\mathit{c}}$ are thermally activated with activation energies of 0.16 and 0.19 eV. When oxygen is reduced to about 6.5 atoms per formula unit, the higher-temperature process nearly disappears, while the other one increases. The peaks are interpreted in terms of jumps of the O atoms in the Cu-O basal planes, and two mechanisms are proposed and discussed: short jumps between the off-center positions in the chains and jumps between O(4) and O(5) positions of isolated atoms in hypothetical oxygen-depleted islands of the orthorhombic basal planes.